Apparatus for analysis and correction of abnormal refractive errors of the eye

ABSTRACT

The invention contemplates instrumentation to aid in performing refraction-corrective surgery on the cornea, (1) by determining the topography of the anterior surface of the cornea, the determination being in the form of digitized data entered into computer storage, (2) by determining the local thickness of the cornea along multiple axes, the determination being also in the form of digitized data entered into computer storage, and (3) by providing a CAD/CAM display of both categories of data, correlated as appropriate for the surgeon&#39;s selective display of a corneal region, aspect or section, as the surgeon may deem pertinent to a prospective operation.

This application is a division of copending application Ser. No.691,923now U.S. Pat. No. 4,669,466 filed Jan. 16, 1985.

BACKGROUND OF THE INVENTION

The invention relates to non-invasive ophthalmogical instrumentation andtechniques for determining physical dimensions of an eye and to theinformed use of thus-derived dimensional data in the performance ofcorrective surgery upon the cornea.

The human eye is an extremely powerful focusing device that produces animage on the surface of the retina. The focusing elements of the eye arethe cornea and the lens. The cornea accounts for approximately 80percent of the focusing ability (48 diopters) and the lens approximately20 percent (12 diopters). In the case of myopia, the eye is assumed tohave a longer egg-like shape in which case the light beam focuses to aspot located in front of the retina and therefore is out of focus. Inhyperopia, the focusing system is inadequate, and the focusing spot andimage are located behind the retina and also out of focus. In the caseof astigmatism, a spot or clear image is not created, and the eyebasically focuses at two areas behind or in front of the retinalsurface. In order to correct myopia, hyperopia, or astigmatism,spectacles or contact lenses are used to place the image directly on therods and cones of the retina. As an alternative to artificial correction(i.e., spectacles, or contact lenses), it has been dembnstrated, asnoted previously, that refractive keratoplasty, surgically altering theshape of the cornea, will achieve the same result.

As alternative techniques of refractive keratoplasty, radial keratotomyand corneal sculpting are the two kinds of corneal surgery which havebeen receiving increased consideration. In radial keratotomy, some 8 to32 radial incisions are applied with a knife to the cornea, and it hasbeen shown that the curvature of the cornea is thereby flattened to adegree which places the focus further back in the eye, hopefully nearthe retinal surface. Such an operation has been demonstrated to improvevision by reducing objective myopia, with a measured improvement of upto 12 diopters. The operation is performed by using a diamond or rubyknife with an adjustable belt or sleeve which controls the depth ofincision to fractions of a millimeter.

The extent of myopia correction is determined by the depth of cut, thenumber of radial incisions, and the proximity of the incisions to thecenter of the cornea. Various other incisions have been combined withradial incisions to achieve other corrective effects, and by combiningcircumferential incisions with radial incisions in various portions ofthe cornea, a characterized flattening of the cornea is possible,whereby a concurrent decrease is achieved in myopia as well as inastigmatism.

Corneal sculpting consists of an advanced procedure, beyond radialkeratotomy, which involves the removal of external layers of the cornea,in such a way as to affect the radius of curvature in order to increaseor decrease the dioptric power of the front surface of the cornea. Byremoving various layers of the cornea to the extent of 0.15 to 0.25millimeters of the 0.60-millimeter thickness of a cornea, up to 12diopters of myopia or hyperopia can be corrected, along with correctionof extremely high degrees of astigmatism (or unevenness of the cornea).By thus sculpting the cornea, in effect, the outer surface of the corneacan have the radius of curvature of a correcting contact lens, as if thecontact lens had been inserted over the malformed cornea. It is theouter surface of the cornea with its air/cornea interface that providesthe increase or decrease in the focal length (power) of the cornea andtherefore alters the refractive state of the eye.

One approach to corneal sculpting has been a procedure termedkeratomileusis, whereby the exterior of the cornea is removed as aplano-convex button, frozen, placed on a microlathe, and shaped by thelathe under computer control until a predetermined curvature of thecornea is achieved. The corneal button is then thawed and sewn back ontothe patient's eye. In this way, the external corneal curvature ischanged by a process of mechanical intervention.

Another approach to corneal sculpting and to radial keratotomy is vialaser incision, as described in my original patent application Ser. No.552,983, filed Nov. 17, 1983 (abandoned, subject to continuingprosecution, eventuating in U.S. Pat. No. 4,665,913). From the aspect ofcorneal scultping, said patent application describes methods andapparatus for changing the anterior surface of the cornea from aninitial curvature having defective optical properties to a subsequentcurvature having correctively improved properties, by using ultravioletlaser radiation to selectively ablate the optically used central area ofthe anterior surface of the cornea by photodecomposition, withpenetration into the stroma and volumetric sculpturing removal ofcorneal tissue to such penetration depth and profile as to characterizethe anterior surface of the cornea with said subsequent curvature. Asexplained in said application, ablation by photodecomposition isphoto-chemical, i.e. the direct breaking of intra-molecular bonds, andall damage adjacent the photodecomposed ablation is insignificant; thisis in sharp contrast with the effect of laser radiation at greaterwavelengths wherein the ablation or incision is thermally achieved,through photocoagulation and/or photovaporization, wherein cellsadjacent the ablated or incised margin are charred.

But no matter what the procedure for operating upon the cornea toachieve refractive correction the fact remains that what has been doneand is being proposed to be done is largely experimental. There is nofund of experience upon which to draw for an acceptably accurateprediction of ultimate refractive correction in the eye, for a giventechnique in application to a given category of corneal dimensions. And,particularly in the case of radial keratotomy, the danger is everpresent that incision will be made to excessive depth, thus aborting theotherwise non-invasive nature of the operation.

BRIEF STATEMENT OF THE INVENTION

It is an object of the invention to provide an improved method andapparatus for use in aid of non-invasive corneal surgery to achieverefractive correction of an eye.

A specific object is to provide the ophthalmological surgeon withcorneal thickness and topography data, for a particular abnormal eye,and in the form of readily interpretable context against which todetermine the depth of surgical incision and the surface distribution ofsurgical incision into the anterior surface of the abnormal cornea, toachieve a desired refractive correction.

Another specific object is to achieve the above objects with a CAD/CAMvisual display of corneal topography and thickness, with selectiveavailability of the display for various attitudes.

Still another specific object is to achieve the above objects with avisual display which also indicates, for selected attitudes, the extentof corneal excision required to achieve a particularrefraction-corrected result, e.g., emmetropia (perfect vision atdistance).

It is also a specific object to meet above objects with computer-aidedmeans for prescribing for a given examined eye the nature and extent ofrefraction-corrective corneal surgery required to achieve or tosubstantially achieve emmetropia for the examined eye.

A further specific object is to meet the above objects withcomputer-aided means whereby digital data are available for control ofautomated apparatus to perform the refraction-corrective surgery.

The foregoing objects and further features are achieved (1) bydetermining the topography of the corneal surface of an eye, thedetermination being in the form of digitized data entered into computerstorage, (2) by determining the local thickness of the cornea alongmultiple axes, the determination being also in the form of digitizeddata entered into computer storage, and (3) by providing a CAD/CAMdisplay of both categories of data, correlated as appropriate for thesurgeon's selective display of a corneal region, aspect or section, ashe may deem pertinent to a prospective operation.

DETAILED DESCRIPTION

The invention will be illustratively described in detail in conjunctionwith the accompanying drawings, in which:

FIG. 1 is a block diagram schematically indicating apparatus andmanipulative steps involved in the invention;

FIGS. 2, 3 and 4 are simplified diagrams to illustrate alternativedisplays at Module C of FIG. 1; and

FIGS. 5 and 6 are simplified diagrams to illustrate alternatives for aCAD/CAM display at Module D in FIG. 1.

The diagram of FIG. 1 depicts all components for performing cornealevaluation and analysis, as well as those involved in incisional orsculpting keratoplasty operations which are based on the analysis.

The evaluation portion is shown to comprise three modules A, B, and C.The first, module A, determines topography of the cornea surface of theeye under consideration. This module may be an optical ocular scanner ora photokeratometer, with provision for generation of digitizedtopography data in an output 10. Module A has the ability to rapidlyscan the cornea in such a way as to determine the entire topography ofthe outer surface of the cornea, from limbus to limbus. In this module,subtle differences in curvature of the outer cornea or inner opticalzone are precisely and clearly defined, and the module will beunderstood to include an analyzer having the capability of digitizingthe data from thousands of individual points on the particular cornea. Asuitable equipment for use in Module A is the PKS-1000 photokeratoscopecommercially available from the Japanese firm, Sun Contact Lens Co.,Ltd., with U.S. offices in Palo Alto, Calif. The Sun photo-keratoscopeis available with a photo-analyzer having a digitized output from whichvisual display is produceable to show the cross-sectional profile ofanterior-surface curvature, for any cross-sections which include thecentral axis of the eye; the connection 10 will be. understood to conveysuch a digitized output.

The second module B comprises pachymetric means for making multipledeterminations of the precise thickness of the cornea, to withinthousandths of a millimeter, at plural locations on the surface of thecornea. The data are generated by ultrasonic-ranging, and are digitizedas to measured thickness correlated with location-coordinate data forsupply in an output 11. The pachymeter measurements may be performedmanually, on an individual point-by-point basis, using a commerciallyavailable hand-held transducer probe flexibly connected to power supplyand display means, for example the Myopach ultrasonic pachymeteravailable from Myocure, Inc., Los Angeles, Calif., or the CILCO, Inc."Villasenor" ultrasonic pachymeter, available from their Huntington,West Virginia location. In using such a device, a fixation targetenables the unexamined eye of the patient to maintain central-axisstability for his examined eye when the probe is placed on the cornealsurface anywhere from the central optical axis to the periphery.

Preferably, a FIG. 3 (i.e., a front-elevation) display is selected, witha manipulable cursor to select and identify the estimated coordinatelocation of each point of pachymeter application to the cornea, an entryof thickness measurement being made into computer storage at module Cfor each different cursor-identified location. Typically, five points ofthickness measurement are taken along each of several selected meridiancourses through the central axis of the eye, and, in the event ofcorneal astigmatism (as is discernable from the FIG. 3 display oftopography data generated by module A), it is recommended that theobserved astigmatism-axis orientation be selected as the orientation fora central meridian of pachymeter measurements, with second and thirdsuccessive sets of pachymeter measurements along meridians which arerespectively offset 20 degrees on opposite angular sides of the centralmeridian of pachymeter measurement. Still further, it is recommendedthat the five pachymeter measurements on the central meridian be taken(a) at each of two outer limits which are about one millimeter short ofintercept with the limbus, (b) at the center (i.e., on the optical axisof the eye), and (c) at the mid-points between the center and each ofthe respective outer limits; for the two meridians which arerespectively at ± 20 degrees offset from the central meridian, only fourmeasurements are recommended (namely, the outer-limit and the mid-pointmeasurements) because the central or optical-axis thickness measurementneed only be made once and therefore would only be repeated if made formore than one meridian sweep.

The third module C comprises a computer supplied by the topographicaldigital data (connection 10 from module A) and by the thickness digitaldata (connection 11 from module B). This computer, which may for examplebe an IBM PC computer, will be understood to have the necessary computerpower to display the evaluated cornea in CAD/CAM fashion within theblock of module C, as alternatively and diagrammatically shown in FIGS.2, 3 and 4. The diagrammatic showing of FIG. 2 is for a full meridiansection of the cornea (at least from limbus to limbus), and it will beunderstood that the computer has the capacity to so enlarge the scale ofthe sectional-display as to enable "close-up" examination of the detailof a selected fragment of the full section, namely as to precise localtopography and thickness of the cornea.

It will be understood that the digital data supplied in connections10-11 to module C lends itself to alternative techniques of CAD/CAMdisplay, as suggested in FIGS. 3 and 4; in FIG. 3, the cornea isdisplayed as if viewed from the anterior-posterior aspect (i.e., fromfront elevation), with alternating rings of progressively increasingthickness, in quantized increments, and in FIG. 4, the cornea isdisplayed as if viewed in perspective, with the isothickness contours ofFIG. 3 shown in their correct perspective. The perspective of FIG. 4,coupled with the ability to selectively rotate the same via suitablesoftware in the computer, will be seen to enable the surgeon to have adirect anterior-posterior viewing of the cornea as created forevaluation on the CRT screen of the computer. It will be furtherunderstood that with suitable software, the various displays of FIGS. 2,3 and 4 may include numerical data which establish the aspect or angleof viewing display, as well as a numerical statement of local corneathickness and/or curvature (anterior and/or posterior surface) and/ordioptric power, for any single point or series of points on the cornealsurface. Such numerical data, as well as any of the various displays,will also be understood to be available for hard-copy print-out of anystage in the evaluation of the cornea.

Module D in FIG. 1 provides an additional CAD/CAM display (e.g., as inFIG. 5 or FIG. 6) which utilizes both the topographical and thicknessmeasurement data supplied to Module C, as well as additional digitizedinformation from another source, such as digitized data pertaining toidealized topography from a Module E, and/or digitized data from anoperative-evaluation data bank, Module F.

Computer storage at Module E, which may be on a diskette usable as asource of data for part of the display at Module D, contains storeddigitized data for the corneal topography of an idealized eye capable ofcreating emmetropia for the eye under evaluation for refractive surgicalkeratoplasty, considering the axial length of the eye determined byA-scan ultrasonography, the age and sex of the patient, intraocularpressure, and other factors which would allow close comparison of theevaluated eye with the projected idealized model emmetropic eye havingsimilar or identical measurable parameters except for the proposedalteration in corneal curvature to obtain emmetropia. And by enteringinto Module E measured parameter data such as the age and sex of thepatient, the axial (anterior-posterior) length of the eye (tenths ofmillimeters), the intraocular pressure of the eye, the resultantrefractive condition desired (e.g., -1.50 diopters, -1.00 diopters,emmetropia, etc.), the desired surgical approach (incisional, such asradial keratotomy, or sculpting, etc.) and a selected data base for theeye (entered via suitable means suggested by Module E') for the eye ofthe present concern, it becomes possible to create at Module D, and fromthe stored digitized data for the idealized eye, an additional displayof the corneal profile of the idealized eye along the meridian selectedfor profile display of measured data at Module D. This feature permitsthe meridian profile for the idealized eye to be comparatively evaluatedwith respect to the display of the meridian profile for the measured-eyedata (from connections 10-11).

More specifically, FIG. 5 illustrates a Module D display wherein themeasured eye is myopic, i.e., wherein the cornea profile 12 for thedisplayed meridian section of the measured eye is more curved and lessflattened than the cornea profile 13 for the displayed meridian sectionof the idealized eye. In this circumstance, it is preferred to so orientthe placement of profile 13 on profile 12 as to cause their near-limbusintersection. Thus, in FIG. 5, the points 14-15 of intersection ofprofiles 12-13 are at symmetrical offset on opposite sides of theoptical axis 16, and the crescent-section area between profiles 12-13represents that which must be excised if keratoplasty is to be by laseror other sculpting reduction of the cornea from profile 12 to profile13. And if keratoplasty is to be by laser or by knife-cut radialkeratotomy, the profile 13 is indicative of the target curvature towhich it is necessary to effect cornea-curvature modification, toachieve or approach post-operative emmetropia.

On the other hand, FIG. 6 illustrates a Module D display wherein themeasured eye is hyperopic, i.e., wherein the cornea profile 12' for thedisplayed meridian section of the measure eye is more flat and lesscurved than the cornea profile 13' for the displayed meridian section ofthe idealized eye. In this circumstance it is preferred to so orient theplacement of profile 13' on profile 12' as to cause their intersectiononly at intersection 17 with the optical axis 16, and the annular shaperepresented by the section area between profiles 12'-13' designates thatwhich must be excised if the cornea is to be sculpted from the sectionprofile 12' to the section profile 13'.

FIG. 1 further indicates that in lieu of the idealized topography dataprovided by Module E, or in suitably averaged conjunction therewith, anadditional Module F may be drawn upon as a data bank, representing thesurgeon's own experience record, from his prior experience records,and/or the totality of such records from a central data bank, servingthe hospitals and ophthalmological facilities of a given geographicarea, or for the country as a whole. Thus, (1) having performed anoperation such as a radial keratotomy, with 8 radial incisions of 3-mmlength, from an inner radial limit of 2-mm, to an outer radial limit of5-mm, and with what he believes with his manual skill was to areasonably uniform depth of 0.52-mm, (2) having used the analysisequipment of FIG. 1 to reexamine the eye after corneal surgery, and (3)finding that he caused the measured-eye profile 12 at selected meridiansections to substantially conform to the idealized eye profile 13, hecan enter into storage at Module F the pertinent parameters of the eyebefore and after surgery, as well as the pertinent parameters of hisoperative procedure. And upon later inspection of the same eye, he cansimilarly enter into storage at Module F any further observations as tolonger-term effects attributable to the operation. Such recorded data,along with the surgeon's use of other techniques to secure the same or asubstantiallly equivalent result for another patient, can also beentered into storage at Module F, so that in the course of time the databank will accumulate a fund of experience from which alternativetechniques and their after-effects can be part of the availablebackground for optimized presurgery decision-making. It will of coursebe understood that the call up of data from Module E and/or from ModuleF for display at Module D may involve graphical two-dimensional displayof selected meridian sections, as well as written display (a) ofpertinent parameters of the relevant eye (before and after surgery), (b)of pertinent parameters and notes of the involved operative procedure,and (c) of observed long-term after-effects.

In the event that the surgeon decides to use automated scanning-laserapparatus, as of the character described in my said copendingapplication Ser. No. 552,983, to perform corneal surgery, whether thecorrection is to reduce or eliminate a myopia or a hyperopia, the storeddecisional data for the pertinent parameters of the operation will beavailable for total adoption (or for adoption with deliberatemodification) via Module D. Thus, an output connection 18 from Module Dto Module G will be understood to show use of such parameters as controlparameters for automated operation of laser-incisional/sculptingdisplacements via Module G. The stored and available parameter datasupplied via connection 18 will be understood to include suchlaser-operating data as power level, exposure rate (i.e., laser-pulserepetition rate), spot size and the like; and of course having performedthe operation, the operating-parameter data as well as the before/aftereye data will be enterable in the data bank at Module F, should thesurgeon decide that the success (or other outcome) of the operationmerits such retention of data.

It will be seen that the described apparatus and methods meet all statedobjects and portend a major change in approach to correction ofcorneal-refractive problems. The objective of the eye measurements isrealized by creating a digitized data base which describes cornealprofiles, illustratively available for display for any of a plurality ofmeridian sections. These data are available in both graphical andwritten display and may be up-graded by experience, to enable awell-informed base for decision-making prior to surgery; the digitizeddecisional data are directly utilizable for the modeling of incisions(whether radial or full sculpture), or to provide automated directionsfor incision or ablative sculpting. The data may be displayed onhard-copy print-out or on a CRT screen as a guide for the surgeon'sincisions, or to direct an incisional or sculpting laser system.

It will be understood that the automated use of Module G lends itself toperform a single operative procedure to effect the entire refractivecorrection indicated by a display as in FIG. 5 or FIG. 6. Alternatively,and certainly until the surgeon has developed full confidence in use ofthe automated surgery available to him, he may opt to modify the surgeryin the conservative direction of excising merely a fraction, e.g., onehalf, of the corneal tissue indicated for removal. In this latter event,he can make another measurement evaluation of the eye before deciding toproceed with the completing half of the total operation. In other words,by following the automated pattern of tissue removal, but only to onehalf the programmed varying depth of ablation, he can see whatrefractive correction was achieved and thus be in a position to judgewhether the remaining half of the total procedure (i.e., secondoperation) should be (a) to the same, (b) to a greater or (c) to alesser fraction of the programmed varying depth.

An important feature of the invention is the data-bank function thatprovides a supplement to measured data from thecorneal-evaluation/analysis Modules A, B and C. Module D enables thecomparative display of the evaluation/analysis data, in contex with thedata-bank output available from Module F. Significantly, these dataenable the computer at Module D to suggest the appropriate length anddepth of radial keratotomy incisions, the placement of "T" incisions orrelaxing limbal incisions, or any combination of all of the incisionalrefractive surgical procedures now available anywhere in the world. Inthis manner, the computer can suggest to the surgeon the course ofsurgical action that would reduce the refractive error--whether it bemyopic, hyperopic, or astigmatic--in order that the eye may be renderedemmetropic or slightly myopic or even slightly hyperopic. In thismanner, the surgeon has the option to accept the recommendation of thecomputer for his surgical intervention on that particular cornea, asobtained from a nation-wide or broad data base. As the surgeon increaseshis prowess and the number of cases performed, his particularmanipulative surgical technique becomes entered in the computer as afunction entirely separate and unique for him. As his individual database increases, the computer can recognize his tendency for a slightlydeeper incision, wider incision, or other peculiarities of thisindividual technique. Therefore, by inserting a plastic "credit-like"card, the computer can be made to recognize the individual surgeon andcall forth his particular data base, or a more general hospital,city-wide, or larger data-base population. All corrective suggestions bythe computer to produce a particular dioptric end result followingsurgery can be displayed in a CAD/CAM fashion and are capable ofhard-copy print-out. Various suggestions by the computer, adopted andcorroborated by the surgeon, can also be printed immediately for use inthe surgical suite.

Although the indicated presently available pachymeters contemplatecorneal thickness measurement at a plurality of locations on the cornealsurface, including plural locations (e.g., five) along a given meridiansection, even this relatively small number of points on a curve will beunderstood to establish a useful presentation of the curve, particularlyin reference to the much more accurately developed topography data forthe anterior surface of the cornea. Thus, the accurate exterior-surfacedata, taken with the relatively few points of pachymeter data, willenable reasonably accurate digitized availablity of the concavetypography of the cornea, should the surgeon see fit to model the samein his CAD/CAM display, whether the modeling be by meridian section(FIG. 2), elevational aspect (FIG. 3), or rotatable 3-D model (FIG. 4).In the latter event, the modeling at FIG. 4 may include "wire-connected"modeling of both the concave and the convex topographies, in eithertrue-scale thickness offset from each other, or in a displayed offsetrelation wherein the measured thickness is exaggerated (but scaled),e.g., at twice or ten times the measured values.

What is claimed is:
 1. In combination, for performing ophthalmologicalsurgery by selective ablation of the optically used central area of theanterior surface of the cornea with penetration into the stroma toachieve a predetermined sculpturing volumetric removal of cornealtissue, said ablation being substantially without formation of scartissue and therefore not impairing the optical transparency of remainingcorneal tissue, a topography-display unit with provision for storage ofdigital data and adapted to present from storage a comparative displayof measured and desired ideal curvatures of the cornea, anultraviolet-laser unit with means to direct ultraviolet radiation to theoptically used central area of the anterior surface of the cornea toselectively ablate the same by photodecomposition, and means connectedto both said units for controlling stroma-penetrating volumetric removalof corneal tissue from the optically used central area in accordancewith the difference between said measured and desired ideal curvaturesof the cornea.
 2. The combination of claim 1, in which said display unitdisplays said curvatures for a meridian section.
 3. Apparatus includinga digital computer to correctively improve optical properties of an eyeby a sculpturing change in curvature of the optically used central areaof anterior surface of the cornea, said apparatus comprising:(a) meansfor determining and digitizing the topography of the optically usedcentral area of the anterior surface of the cornea as athree-dimensional curved surface, and for entering digitized topographydata thereof into computer storage; (b) means for digitally defining andentering into computer storage, as another three-dimensional curvedsurface, digitized data for the anterior-surface topography of anidealized cornea wherein optical improvement is the achievementobjective based on measured parameter data for the eye, whereby computerstorage contains digitized data which is definitive of a characterizedvolumetric removal necessary to proceed from one to the other of saidcurved surfaces; (c) means including an ultraviolet laser for directingultraviolet laser radiation to the optically used central area of theanterior surface of the cornea to selectively ablate the same byphotodecomposition, said ablation being substantially without formationof scar tissue and therefore not impairing the optical transparency ofremaining corneal tissue; and (d) laser-control means connected forresponse to said computer-storage data to control the laser radiation toachieve said other curved surface in a sculpturing volumetric removal oftissue from the optically used central area of the anterior surface andwith penetration into the stroma.
 4. Apparatus including a digitalcomputer to correctively improve optical properties of an eye by asculpturing change in curvature of the optically used central area ofthe anterior surface of the cornea in approach to but short of acomputer-stored digital definition of an idealized three-dimensionalanterior-surface curvature, said apparatus comprising:(a) means fordetermining and digitizing the topography of the anterior surface of thecornea as a three-dimensional curved surface, and for entering digitizedtopography data thereof into computer storage; (b) means for creatingfrom said topography data and from said stored digital definition adisplayed numerical statement of the spherical and cylindricalcomponents of difference between the determined and the idealizedcurvatures, whereby the displayed numerical statement is also astatement which is definitive of a characterized volumetric removal ofcorneal tissue necessary to proceed from the determined to the idealizedcurvature; (c) means including an ultraviolet laser for directingultraviolet radiation to the optically used central area of the anteriorsurface of the cornea to selectively ablate the same byphotodecomposition, said ablation being substantially without formationof scar tissue and therefore not impairing the optical transparency ofremaining corneal tissue; and (d) lasser-control means connected forresponse to said computer-storage data to control the laser radiation toachieve a curvature change in approach to but short of the idealizedsurface curvature in a sculpturing volumetric removal of tissue from theoptically used central area of the anterior surface and with penetrationinto the stroma.
 5. The apparatus of claim 4, in which said numericalstatement is in diopters.
 6. Apparatus including a digital computer tocorrectively improve optical properties of an eye by a sculpturingchange in curvature of the optically used central area of the anteriorsurface of the cornea, said apparatus comprising:(a) means fordetermining and digitizing the topography of the anterior surface of thecornea as a three-dimensional curved surface, and for entering digitizedtopography data thereof into computer storage; (b) display meansincluding means for creating from the stored digitized topography data acenter-identified display of the front elevation of the cornea; (c) saiddisplay means further including selectively operable means for creatingon said display a straight marker line along a meridian through thecenter of the display and at a selected orientation; (d) means forentering into computer storage digitized data for the corneal topographyof an idealized eye wherein emmetropia is the achievement objective; (e)said display means still further including means for creating from thestored digitized data for the measured eye and for the idealized eye acoordinated display of both measured and idealized curvatures along saidmeridian, whereby computer storage contains digitized data which isdefinitive and said coordinated display is visually indicative of acharacterized volumetric removal of corneal tissue necessary to proceedfrom the measured curvature toward the idealized curvature; (f) meansincluding an ultraviolet laser for directing ultraviolet laser radiationto the optically used central area of the anterior surface of the corneato selectively ablate the same by photodecomposition, said ablationbeing substantially without formation of scar tissue and therefore notimpairing the optical transparency of remaining corneal tissue; and (g)said last-defined means being responsive to said computer-storage datato control the laser radiation to approach the idealized curvature in asculpturing volumetric removal of tissue from the optically used centralarea of the anterior surface and with penetration into the stroma. 7.Apparatus according to claim 6, wherein said display means includesmeans for selectively rotating the meridian marker line about the centerof the display, whereby astigmatism can be visually apparent in saidcoordinated display.
 8. Ophthalmic apparatus for use in correctivelyimproving optical properties of an eye by a sculpturing change incurvature of the optically used central area of the anterior surface ofthe cornea, said apparatus comprising:(a) a topography-measuringcomponent including means providing digitized output data reflectingmeasured topography of the optically used central area of the anteriorsurface of the cornea; (b) an idealized-topography component includingmeans providing digitized output data reflecting a desired topography ofthe optically used central area of the anterior surface of the cornea;(c) storage means connected to the respective outputs of said componentsfor storage of their respective digitized output data; (d) display meansincluding a computer connected to said storage means for producing acomputer-aided and coordinate display of measured and desiredtopographic data; (e) a cornea-sculpting photo-ablative ultravioletlaser for directing laser radiation to the optically used central areaof the cornea, said ablation being substantially without formation ofscar tissue and therefore not impairing the optical transparency ofremaining corneal tissue, and laser-control means operatively connectedto said storage means for differential response to the differencebetween said measured and desired topographic data.
 9. Ophthalmicapparatus for use in correctively improving optical properties of an eyeby a sculpturing change in curvature of the optically used central areaof the anterior surface of the cornea, said apparatus comprising:(a) atopography-measuring component including means providing digitizedoutput data reflecting measured topography of the anterior surface ofthe cornea; (b) an idealized-topography component including meansproviding digitized output data reflecting a desired topography of theanterior surface of the cornea; (c) storage means connected to therespective outputs of said components for storage of their respectivedigitized output data; (d) display means including a computer connectedto said storage means for producing a computer-aided and coordinateddisplay of measured and desired topographic data; (e) an ultravioletlaser-sculpturing means for directing ultraviolet radiation to theoptically used central area of the anterior surface of the cornea toselectively ablate the same by photodecomposition, said ablation beingsubstantially without formation of scar tissue and therefore notimpairing the optical transparency of remaining corneal tissue; and (f)said laser-sculpturing means including control means operativelyconnected to both said storage means for producing a sculpturingvolumetric removal of tissue from the optically used central area of theanterior surface and with penetration into the stroma, said volumetricremoval being in accordance with the curvature difference between storeddata for the respective outputs of said components.
 10. The apparatus ofclaim 9, in which said display means produces a sectional display of themeasured and desired topographic data, wherein the display superposesthe central axis of the measured section and the central axis of thedesired section.
 11. The apparatus of claim 10, in which said displaymeans includes selectively operable means for displacing, in thedirection of the superposed central axes, the measured-section displayand the desired-section display with respect to each other. 12.Ophthalmic apparatus for use in correctively improving opticalproperties of an eye by a sculpturing change in curvature of theoptically used central area of the anterior surface of the cornea, saidapparatus comprising:(a) a topography-measuring component includingmeans providing digitized output data reflecting measured topography ofthe anterior surface of the cornea; (b) an idealized-topographycomponent including means providing digitized output data reflecting adesired topography of the anterior surface of the cornea; (c) storagemeans connected to the respective outputs of said components for storageof their respective digitized output data; (d) an ultravioletlaser-sculpturing means for directing ultraviolet radiation to theoptically used central area of the anterior surface of the cornea toselectively ablate the same by photodecomposition, said ablation beingsubstantially without formation of scar tissue and therefore notimpairing the optical transparency of remaining corneal tissue; and (e)said laser-sculpturing means including control means operativelyconnected to both said storage means for producing a sculpturingvolumetric removal of tissue from the optically used central area of theanterior surface and with penetration into the stroma, said volumetricremoval being in accordance with the digital difference between storeddata for the respective outputs of said components.